Online Mendelian Inheritance in Man (OMIM.) is a knowledgebase of genetic disorders and genes. Initially created by Dr. Victor McKusick in 1966 as Mendelian Inheritance in Man, OMIM has been freely available on the internet/web since 1987. In December 2010, omim.org, funded by Johns Hopkins University, went live, hosted by UCSC Genome Informatics. OMIM is the premier resource for clinical geneticists and for researchers in molecular biology, genetics, and genomics. With detailed descriptions of over 7,000 disorders and more than 13,600 genes, OMIM has an unparalleled breadth and richness of description of human phenotypic variation. OMIM's stability and authority are internationally recognized, and MIM numbers are required by most human genetics journals. Thousands of users access OMIM daily from around the world. OMIM includes the Morbid Map of the Human Genome, which catalogs the relationship between human disorders (~4300) and the genes (~2500) that cause them. The other ~3000 disorders in OMIM whose molecular basis is currently unknown, as well as disorders not yet defined, will quickly yield to the application of genome-wide sequencing. OMIM is uniquely positioned to organize and present this onslaught of new biomedical information. We plan to collaborate with Mendelian sequencing centers and act as a portal to facilitate the collection of families with Mendelian disorders and to make the results of those studies available through OMIM. To facilitate data mining of OMIM, we have added 1CD9/10 and SNOMEDCT numbers to OMIM entries and plan to add UMLS, SNOMED, HPO and other ontology classifications to the features of OMIM's clinical synopses. OMIM staff members have extensive experience on the project and provide expertise that is critical in elucidating the complexity of human Mendelian diseases and their classification. OMIM will continue to develop and provide authoritative and timely support to the practice of genomic medicine.